1. Field of the Invention
The present invention relates to an optical data storage system, and more particularly to a near-field optical data storage system which can write or read information at high density with respect to an optical storage medium.
2. General Background
An optical data storage system mainly includes an optical pickup and a near-field. The optical pickup has a solid immersion optical system or a solid immersion lens. The near-field is provided between the solid immersion optical system or solid immersion lens and the optical data storage medium. The optical pickup using the near-field performs writing and/or reading of information with respect to the optical data storage medium.
Referring to FIG. 4, a conventional optical data storage system includes a light transmission and reception portion 20, a reflective mirror 22, a focusing objective lens 24, and a refractive solid immersion lens 26 supported by a slider 28. The optical storage medium 18 includes a substrate 181, a protective layer 183, and a recording layer (not shown) between the substrate 181 and the protective layer 183. The slider 28 aerodynamically floats the solid immersion lens 26, whereby an air gap is formed between the solid immersion lens 26 and the optical storage medium 18. The air gap is an interval within one wavelength of the light used. In the optical data storage system, a near-field generating portion is defined at a predetermined position on the surface of the solid immersion lens 26 which opposes the optical storage medium 18. A beam spot is formed in the near-field generating portion.
In operation, the light transmission and reception portion 20 emits light beams having an optimized spread-width for the objective lens 24, the reflective mirror 22 reflects the light beams toward the objective lens 24, and the objective lens 24 focuses the light beams on the solid immersion lens 26. In the case that the interval of the air gap is sufficiently smaller than one wavelength of the light beams, such as λ/4, the spot size of the light beams incident to the optical storage medium 18 is close to the size of the beam spot formed in the near-field generating portion. Therefore, the optical data storage system can write or read information with respect to the recording layer of the optical storage medium 18, using the solid immersion lens 26.
However, because the spot size of the light beams incident to the optical storage medium 18 is close to the size of the beam spot formed in the near-field generating portion, the size of the beam spot is too large to write or read information at higher density with respect to the optical storage medium 18.
What is needed, therefore, is an optical data storage system which can write or read information at higher density with respect to the optical storage medium.